There is a known structure in which a clutch release mechanism moves a clutch piston away from a clutch inner (moves it to a clutch disconnected position), thereby disconnecting a clutch. The clutch piston is urged toward the clutch inner (toward a clutch connected position) by a disc spring. When the clutch release mechanism is out of operation, the clutch is brought into a connected state by the urging force of the disc spring.
With this structure, the relationship between the moving distance and clutch capacity of a member for moving the clutch piston can be set to be linear, and therefore the clutch capacity can be easily controlled by the moving distance of the member. See JP-A No. 2005-249083.